GPIO模拟I2C是嵌入式中较为常用的一种应用。各个地方有各种不同的做法,按照我自己的个人理解,最好是把I2C的各种状态分割开来,比如起始条件终止条件,读数据和写数据,然后根据具体的使用场合组合起来。
这里需要注意两点:一是SCL的波形并不规律,不能将它理解为方波,它本身只是一段段独立的波形。二是每段操作时,之前和之后的SCL和SDA波形是可以忽略的;通常情况下I2C开始之前和I2C结束之后,两者都是有上拉的高电平,而在正常工作时两者不受控制的情况下都是默认低电平。三是I2C是要默认外部上拉的,但是不能有内部上拉也就是必须内部下拉,否则会出现I2C传输时的错误。
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(1)基础宏定义
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#define GPIO_SCL S3C2410_GPF3
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#define GPIO_SDA S3C2410_GPF0
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#define GPIO_SDA_OUTP S3C2410_GPF0_OUTP //设定SDA输出
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#define GPIO_SDA_INP S3C2410_GPF0_INP //设定SDA输入
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#define GPIO_SCL_OUTP S3C2410_GPF3_OUTP //设定SCL输出
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void I2C_SCL_OUTP( void )
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{
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s3c2410_gpio_cfgpin(GPIO_SCL,GPIO_SCL_OUTP);
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}
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void I2C_SCL_Output(u8 value)
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{
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if(value)
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{
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s3c2410_gpio_setpin(GPIO_SCL,value);
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}
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else
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{
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s3c2410_gpio_setpin(GPIO_SCL,value );
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}
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}
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void I2C_SDA_Mode(u8 v_mode) //SDA输出方向
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{
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if(v_mode)
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{
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s3c2410_gpio_cfgpin(GPIO_SDA, GPIO_SDA_OUTP);
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}
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else
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{
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s3c2410_gpio_cfgpin(GPIO_SDA, GPIO_SDA_INP);
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}
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}
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void I2C_SDA_Output(u8 value)
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{
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if(value)
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{
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s3c2410_gpio_setpin(GPIO_SDA,value);
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}
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else
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{
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s3c2410_gpio_setpin(GPIO_SDA,value );
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}
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}
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u8 I2C_SDA_Read(void) //SDA读数据
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{
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return s3c2410_gpio_getpin(GPIO_SDA);
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}
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(2)基础段
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void I2C_Init(void)
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{
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I2C_SDA_Output(1);
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I2C_SCL_Output(1); //默认拉高
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}
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void I2C_Wait(void)
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{
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u16 i;
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for(i=0;i<200;i++);
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}
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void I2C_Start(void)
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{
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I2C_SDA_Output(1);
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I2C_SCL_Output(1);
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I2C_Wait();
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I2C_SDA_Output(0);
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I2C_Wait();
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I2C_SCL_Output(0);
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}
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void I2C_Stop(void)
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{
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I2C_SDA_Output(0);
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I2C_Wait();
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I2C_SCL_Output(1);
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I2C_Wait();
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I2C_SDA_Output(1);
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}
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(3)读写单个字节的段
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u8 I2C_Send_Byte(u8 bytedata)
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{
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u8 i,ack;
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I2C_SDA_Mode(1); //SDA输出
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I2C_SCL_OUTP();
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for (i = 0; i < 8; i++)
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{
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if (bytedata & 0x80)
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{
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I2C_SDA_Output(1);
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}
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else
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{
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I2C_SDA_Output(0);
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}
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bytedata <<= 1;
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I2C_SCL_Output(1);
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udelay(3);
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I2C_SCL_Output(0);
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udelay(1);
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}
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I2C_SDA_Output(1); //release
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udelay(3);
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I2C_SDA_Mode(0); //设定SDA输入
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I2C_SCL_Output(1);
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udelay(3);
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ack = I2C_SDA_Read(); //读应答
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I2C_SDA_Mode(1);
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I2C_SCL_Output(0);
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udelay(3);
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return ack;
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}
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u8 I2C_Receive_Byte(void)
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{
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u8 i;
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u8 bytedata = 0x00;
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u8 temp;
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I2C_SDA_Mode(0);
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for ( i = 0; i < 8; i++)
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{
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I2C_SCL_Output(1);
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udelay(3);
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bytedata <<= 1;
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temp = I2C_SDA_Read();
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printk("reda SDA'value is:%d/n",temp);
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if (temp)
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bytedata |= 0x01;
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printk(" bytedata is:%x/n",bytedata);
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I2C_SCL_Output(0);
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udelay(1);
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}
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I2C_SDA_Mode(1);
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return bytedata;
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}
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(4)读写单个字节的I2C应用函数
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u8 I2C_Byte_Write(u8 device_ID,u8 address,u8 bytedata)
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{
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u8 ack;
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printk("device_ID is:%x/n",device_ID);
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printk("address is:%x/n",address);
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printk("date is:%x/n",bytedata);
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I2C_Start();
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ack=I2C_Send_Byte(device_ID);
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printk("ack is:%d/n",ack);
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if(ack)
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I2C_Stop();
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I2C_Send_Byte(address);
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I2C_Send_Byte(bytedata);
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I2C_Stop();
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I2C_Wait();
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return 0;
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}
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u8 I2C_Byte_Read(u8 device_ID,u8 address)
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{
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u8 bytedata;
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I2C_Start();
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I2C_Send_Byte(device_ID);
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I2C_Send_Byte(address);
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I2C_Start();
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I2C_Send_Byte(device_ID+1);
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bytedata = I2C_Receive_Byte(); //读单个字节,不需要再发应答
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I2C_Stop();
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return bytedata;
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}
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(5)类似可以完成读写多个字节的函数,暂不补充。
第二种方式也可以用
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#ifdef I2C_USE_GPIO
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#define GPIO_I2C_DEBUG
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#define GPIO_I2C_SDA_PIN GPIO_I2C1_SCA_PIN
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#define GPIO_I2C_SCA_PIN GPIO_I2C1_SDA_PIN
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#define GPIO_SDA_OUTP mt_set_gpio_dir(GPIO_I2C_SDA_PIN,GPIO_DIR_OUT) //设定SDA输出
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#define GPIO_SDA_INP mt_set_gpio_dir(GPIO_I2C_SDA_PIN,GPIO_DIR_IN) //设定SDA输入
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#define GPIO_SCL_OUTP mt_set_gpio_dir(GPIO_I2C_SCA_PIN,GPIO_DIR_OUT) //设定SCL输出
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#define I2C_SDA_Output(value) mt_set_gpio_out(GPIO_I2C_SDA_PIN,value)
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#define I2C_SCL_Output(value) mt_set_gpio_out(GPIO_I2C_SCA_PIN,value)
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#define DELAY_TIME 0xc0
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u8 I2C_SDA_Read(void) //SDA读数据
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{
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return mt_get_gpio_in(GPIO_I2C_SDA_PIN);
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}
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void I2C_Init(void)
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{
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mt_set_gpio_mode(GPIO_I2C_SDA_PIN,GPIO_MODE_00);
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mt_set_gpio_mode(GPIO_I2C_SCA_PIN,GPIO_MODE_00);
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GPIO_SDA_OUTP;
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GPIO_SCL_OUTP;
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I2C_SDA_Output(1);
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I2C_SCL_Output(1); //默认拉高
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}
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#define I2C_START_TRANSMISSION
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{
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volatile u8 idx;
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GPIO_SCL_OUTP;
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GPIO_SDA_OUTP;
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I2C_SDA_Output(1);
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for (idx = 0; idx < DELAY_TIME; idx++);
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I2C_SCL_Output(1);
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for (idx = 0; idx < DELAY_TIME; idx++);
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I2C_SDA_Output(0);
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for (idx = 0; idx < DELAY_TIME; idx++);
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I2C_SCL_Output(0);
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}
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#define I2C_STOP_TRANSMISSION
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{
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volatile u8 idx;
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GPIO_SCL_OUTP;
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GPIO_SDA_OUTP;
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I2C_SCL_Output(0);
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I2C_SDA_Output(0);
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for (idx = 0; idx < DELAY_TIME; idx++);
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I2C_SCL_Output(1);
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for (idx = 0; idx < DELAY_TIME; idx++);
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I2C_SDA_Output(1);
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}
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static kal_uint8 I2C_Send_Byte(kal_uint8 send_byte)
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{
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volatile signed char i = 0;
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volatile kal_uint16 j = 0;
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kal_uint8 ack = 0;
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for (i = 7; i >= 0; i--)
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{
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if (send_byte&(1 << i))
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{
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I2C_SDA_Output(1);
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}
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else
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{
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I2C_SDA_Output(0);
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}
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(1);
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for (j = 0; j < DELAY_TIME; j++);
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GPIO_SDA_OUTP; /* only for delay */
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(0);
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for (j = 0; j < DELAY_TIME; j++);
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}
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GPIO_SDA_INP;
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(1);
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for (j = 0; j < DELAY_TIME; j++);
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ack = I2C_SDA_Read();
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(0);
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for (j = 0; j < DELAY_TIME; j++);
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GPIO_SDA_OUTP;
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return ack;
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}
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static kal_uint8 I2C_Receive_Byte(void)
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{
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volatile signed char i = 0;
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volatile kal_uint16 j = 0;
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kal_uint8 get_byte = 0;
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GPIO_SDA_INP;
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for (j = 0; j < DELAY_TIME; j++);
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for (i = 7; i >= 0; i--) { // data bit 7~0
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I2C_SCL_Output(1);
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for (j = 0; j < DELAY_TIME; j++);
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if (I2C_SDA_Read()) {
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get_byte |= (1 << i);
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}
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(0);
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for (j = 0; j < DELAY_TIME; j++);
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}
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// don't care bit, 9th bit
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GPIO_SDA_OUTP;
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I2C_SDA_Output(1);
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(1);
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(0);
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return get_byte;
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}
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static kal_uint16 I2C_Receive_word(void)
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{
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volatile signed char i = 0;
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volatile kal_uint32 j = 0;
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kal_uint16 get_byte = 0;
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for (i = 15; i >= 8; i--)
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{
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GPIO_SDA_INP;
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(1);
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for (j = 0; j < DELAY_TIME; j++);
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if (I2C_SDA_Read()) get_byte |= (1 << i);
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(0);
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for (j = 0; j < DELAY_TIME; j++);
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}
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I2C_SDA_Output(0);
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GPIO_SDA_OUTP;
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for (j = 0;j < DELAY_TIME; j++);
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I2C_SCL_Output(1);
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for (j = 0;j < DELAY_TIME; j++);
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GPIO_SDA_OUTP; /* just for delay */
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for (j = 0;j < DELAY_TIME; j++);
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I2C_SCL_Output(0);
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for (j = 0;j < DELAY_TIME; j++);
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for (; i >= 0; i--)
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{
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GPIO_SDA_INP;
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(1);
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for (j = 0; j < DELAY_TIME; j++);
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if (I2C_SDA_Read()) get_byte |= (1 << i);
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for (j = 0; j < DELAY_TIME; j++);
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I2C_SCL_Output(0);
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for (j = 0; j < DELAY_TIME; j++);
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}
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I2C_SDA_Output(1);
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GPIO_SDA_OUTP;
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for (j = 0;j < DELAY_TIME; j++);
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I2C_SCL_Output(1);
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for (j = 0;j < DELAY_TIME; j++);
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GPIO_SDA_OUTP; /* just for delay */
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for (j = 0;j < DELAY_TIME; j++);
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I2C_SCL_Output(0);
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for (j = 0;j < DELAY_TIME; j++);
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return get_byte;
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}
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u8 I2C_Byte_Write(u8 * a_puBuff , u8 len , u8 i2c_addr)
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{
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kal_uint8 fail_try_no = 4;
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volatile signed char i = 0 ;
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u8 ack_flag = 0;
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while (--fail_try_no > 0)
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{
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ack_flag = 0;
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I2C_START_TRANSMISSION;
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if (I2C_Send_Byte(i2c_addr)) continue;
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for(i = 0 ;i < len;i++){
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if (I2C_Send_Byte(a_puBuff[i])){
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ack_flag = 1;
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break;
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}
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}
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if(ack_flag)
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continue;
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break;
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}
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I2C_STOP_TRANSMISSION;
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return 0;
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}
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u8 I2C_Bytes_Read(u8 *a_puBuff, u8 reglen ,u8 *byteget,u8 bytelen,u8 i2c_addr)
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{
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kal_uint16 get_byte = 0xFFFF;
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kal_uint8 fail_try_no = 4;
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volatile kal_uint32 i = 0;
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u8 ack_flag = 0;
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while (--fail_try_no > 0)
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{
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ack_flag = 0;
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I2C_START_TRANSMISSION;
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if (I2C_Send_Byte(i2c_addr)) continue;
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//send reg
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for(i = 0 ;i < reglen;i++){
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if (I2C_Send_Byte(a_puBuff[i])){
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ack_flag = 1;
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break;
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}
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}
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if(ack_flag)
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continue;
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I2C_START_TRANSMISSION;
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if (I2C_Send_Byte(i2c_addr | 1)) continue;
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if(bytelen == 1)
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byteget[0] = get_byte = I2C_Receive_Byte(); //读单个字节,不需要再发应答
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else if(bytelen > 1)
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{
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get_byte=I2C_Receive_word();
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byteget[1] = get_byte & 0x00ff;
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byteget[0] = (get_byte & 0xff00) >> 8;
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}
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break;
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}
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I2C_STOP_TRANSMISSION;
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printk("----%s---read data %x---n",__func__,get_byte);
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return get_byte;
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}
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int iWriteRegI2C(u8 *a_pSendData , u16 a_sizeSendData, u16 i2cId)
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{
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I2C_Byte_Write(a_pSendData,a_sizeSendData,i2cId);
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return 0;
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}
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int iReadRegI2C(u8 *a_pSendData , u16 a_sizeSendData, u8 * a_pRecvData, u16 a_sizeRecvData, u16 i2cId)
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{
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